The invention may be applied advantageously, but is not limited to, the reading of an optical signal, in particular in optical disk reader systems. In these systems, the processing circuit is situated between a photodetector and an analog-digital converter to adapt the signal coming from the photodetector to the input range of the analog-digital converter. The amplitude of the incident voltage can vary depending on the quantity of light emitted by the reader system laser and received by the processing circuit. This quantity of light can vary because of defects in optical disks and voltage offsets generated by the various components of the circuit.
An approach developed by the Applicant in the Patent FR-2 820 307 proposes an asymmetric processing circuit. This processing circuit, with ‘single-end’ architecture, notably has a variable-gain converter followed by a current/voltage converter. But, at the output of the current/current converter, the current level can be very high and incompatible with the input range of the voltage/current converter. This circuit therefore includes two compensation circuits as an approach to this problem. However, such an approach turns out to be relatively complex to implement. Moreover, such a processing circuit is a source of harmonic distortion. In addition, it has a relatively low noise-rejection ratio and the structure has a stability problem at very high frequency.